1. Field of the Invention
The present invention relates to a circuit apparatus and, more particularly, to a circuit apparatus provided with an electrode pad.
2. Description of the Related Art
With portable electronic appliances such as cell phones, PDAs, DVCs and DSCs becoming more and more advanced in their capabilities, miniaturization and weight reduction of products have become essential for market acceptance. Accordingly, highly-integrated system LSIs for achieving these goals are demanded. Since ease and convenience of use are required of these electronic appliances at the same time, high capabilities and high performance are essential requirements for LSIs used in these appliances. While the number of I/Os is increasing as a result of increasingly high integration of LSI chips, there is also a persistent requirement for miniaturization of packages themselves. In order to meet the requirements for high integration and miniaturization, development of a semiconductor package adapted for high-density packaging of semiconductor components on a substrate is called for. A packaging technology called chip size packaging (CSP) has been developed in a variety of forms to address these requirements.
Ball grid array (BGA) is known as an example of package adapted for such requirements. A BGA is formed such that semiconductor chips are mounted on a package substrate and then molded by resin. Solder balls are formed as terminals for connection to external apparatuses in selected areas on the opposite side.
FIG. 18 is a schematic sectional view of a semiconductor apparatus of BGA type according to the related art. The semiconductor apparatus (circuit apparatus) is configured such that a semiconductor element (circuit element) 106 is mounted on one surface of a circuit substrate 110 and solder balls 112 as terminals for connection to external apparatuses are bonded to the other surface. A wiring pattern 103 (pad electrode par 103a) for electrical connection with the semiconductor element 106 is provided on one surface of the circuit substrate 110. A land part 103b for bonding the terminal for connection to an external apparatus is provided on the other surface of the circuit substrate 110. Electrical connection between the wiring pattern 103 and the land part 103b is established via a conductor part provided on the interior wall of a through hole 111 running through an insulating substrate 101. A solder resist 105 protects the surface of the circuit substrate 110. One surface of the circuit substrate 110 is encapsulated by a sealing resin layer 108 after the semiconductor 106 is mounted.
FIG. 19 is a sectional view showing a pad electrode part (cross section indicated by X in FIG. 18) of the semiconductor apparatus shown in FIG. 18 on an enlarged scale. The pad electrode part 103a wire bonded to the semiconductor element 106 comprises a wiring part formed of copper and a gold plating layer 104 covering the surface of the wiring part. The solder resist layer 105 covers the copper wiring part in the pad electrode part 103a and also covers a portion of the gold plating layer 104. An opening in the solder resist 105 is encapsulated by the sealing resin 108 along with the semiconductor element 106 after the semiconductor element 106 is mounted and wire bonded.
As described in the document, it is important to ensure intimate contact (prevent exfoliation) between the pad electrode part 103a and the sealing resin layer 108 as the semiconductor element 106 is encapsulated by the sealing resin layer 108. If the intimacy of contact in the above-mentioned location is improper, the semiconductor apparatus (circuit apparatus) is affected by thermal stress and humidity, resulting in reduced reliability of the apparatus.